There is a continued effort to reduce leading edge Integrated Circuit (IC) chip area (by improving the circuit density) for cost, yield, and performance benefits. Current e-fuse structures and manufacturing methodologies are not conducive to these goals.
An exemplary use of fuses in semiconductor devices has been in redundancy technology. Redundancy technology improves the fabrication yield of high-density semiconductor devices, such as static random access memory (“SRAM”) devices and dynamic random access memory (“DRAM”) devices, by facilitating the substitution of a redundant program circuit for a failed program circuit that could otherwise render the semiconductor device useless. The failed circuit may be bypassed and the redundant circuit activated or programmed by selectively programming, or “blowing” fuses of the semiconductor device.
Fuses are probably the simplest and most compact mechanism of programming a semiconductor memory device. In conventional designs, the fuse includes a conductive layer, typically comprising metal or polysilicon, which is narrowed in one region. To blow the fuse, a high electrical current (programming current) is applied to the fuse which heats the metal or polysilicon of the fuse to a temperature above the melting point which, in turn, “blows” the fuse, i.e., the metal or polysilicon becomes discontinuous, breaking the conductive link across the fuse. In most instances, the fuse becomes discontinuous at the narrowed region since the current density is highest and the temperature increases most quickly at the narrowed region of the fuse.
When a metal fuse is disposed adjacent a doped silicon or doped polysilicon structure to bridge selected regions thereof, the resistance of the adjacent silicon or polysilicon should not differ significantly from the resistance of the fuse. Thus, upon “blowing” the fuse, the adjacent silicon or polysilicon may continue to transmit current similar to the current carried across an intact fuse. This is especially problematic when a fuse is disposed adjacent an n-well, of a semiconductor substrate conductively doped to have a first conductivity type to bridge two separate conductive wells, such as p-wells, of a second conductivity type, opposite the first conductivity type, disposed adjacent the region of first conductivity type. If the fuse “blows” in a manner that leaves a section of a second, or outlet, side of the fuse that overlaps both a p-well and a portion of the common n-well, current may continue to pass into a p-well from a first side of the “blown” fuse, into the n-well, and out of the n-well to the portion of the second side of the “blown” fuse that overlaps the n-well. Thus, a fuse that blows in such a manner may undesirably conduct current having substantially the same characteristics as current conducted across an intact fuse.